Magnetic record wiper



DeC- 422,l 1931- c. w.. RHODEHAMEL 1,837,586

MAGNETIC RECORD WIPER Filed Feb. 4, 1929 Patented Dec. 22, 1931 CARL W.RHQDEHAMEL, O HOLLYWOOD, CALIFORNIA MAGNETIC RECORD WIPER.

Application led February 4, 1929. Serial- No. 337,519.

My invention relates to magnetic recorders of electrical impulses, andparticularly to a method and apparatus for wiping the record, i. e., forremoving from the record, pre- 5 paratory to making a recording thereon,of such non-uniform magnetic Vpolarizations as it may carry. Thesepolarizations may result either from a previous intentional recording orfrom accidental inuences to which it has l been subjected in the courseof manufacture or handling. Whatever the source of such polarizations,they will be referred to herein as recordings.

An object of my invention is to provide a l means of removing previousrecordings more completely than has hitherto been possible.

Another object of vmy invention is to pro-` vide a means of preparing amagnetic record for receiving a recording in such a manner 2o thatmechanical vibrations of the record will ifiot appreciably aiect thereproduction there- Still another object of my invention is to provide ameans of wi ing the record such that even though resi ual polarizationsbe leftupon the record, they will be of such a nature as tohavesubstantially no elect uponv reproduction therefrom. l

My invention possesses other objects and 3o valuable features, some ofwhich will-be set forth in the following description of my inventionwhich isillustrated in the-drawing forming part of the specification. Itisto be understood that I do not limit myself to the i showing made bythe said description and' drawing, as I may adopt varying forms of myinvention within the scope of the claims.'

Ma etic records of electrical impulses are made y passin a steel wire,tape or disc at 40. a constant rate tween the polepieces of anelectromagnet or ma a current corresponding to the impulses to berecorded. This polarizes elementary portions of the record, and Aif theimpulses are cyclic incharacter, as is ordinarily the case, each cycleoccupies a space on the record which is equal tothe speed with which therecord is traversed divided by the freuency of the impulses. This s acemay v e called the record wave-lengt of the impulse. Ingen- `ing beremoved, and another recording formed on thesame steel.

, polarization.

vention overcomes these diculties. ets, whose coils carry eral thepolarizations are transverse to the direction of travel of the record,or of the recording coil if ther record be the stationary member.Reproduction is accomplished b`y moving the record between thepolepieces ofa magnet similar to that with which the recording was made.This causes a changing flux thru the windings of the magnet, and ifsuitable reproducing mechanism s connected to its terminals, theoriginal impulses are duplicated therein. l

This system finds its primary use in the recording of telephonie orsoundim ulses, but it is also applicable to the repro uction oftelegraphic, televisional or other cyclic or transient impulses.

One ofthe advantages of this method of recording is that the record maybe wiped, i. e., the polarizationsicomprising the record- This permi ofcorrections to a record, and

also greatly reduces thecost when the 'rel cording is neededf-ortemporary use only. In the. past the wiping has been accomplished byrunning the record over the poles of a magnet, thus impressing on. it anunvarying I have found, however, that a record soA wiped will set upundesired and interferent potentials in the reproducing coils as aresult of mechanical vibrations, and that subsequent recordings areVmasked byl noises which are not present if the record is initially ina' wholly unmagnetizedstate. Moreover, it is very difficult to removecompletely all former recordings by this method, and ghost recordingsconse uently remain to confuse the later repro uctions. My in-Referring-to the drawing: 'l

The ligure is alongitudinal sectional view of'anembodiment of myinvention adapted for wiping a ma eticrecord offthe wire. type. Portions`o the electrical circuit are shown schematically. l

'Broadly considered, my-method of wiping the lrecord comprisesdemaxetizing the v record, the demagnetizing field in referably paralleltothe direction in w ich the 109 55 tense at the end where-the wireenters and record is traversed in recording and reproduction, and havinga re'cord wave length' less than that of the highest frequencies that 1nmy apparatus by traversing the record with a spatially graduatedalternating.

magnetic iield at a rate such that the space traversed on the record bythe field during a single cycle is less than the space required for therecording-of a cycle of the highest frequency to be reproduced.

'lhe embodiment of my invention which I have chosen for. detaileddescription is adapted particularl to wiping a wire record, as this isthe orm of magnetic record which in ractice has proved the mostgenerally use ul. y

The wiping device may conveniently be made interchangeable with therecording and reproducing coil box on a wire handling mechanism.comprising essentially a frame 6 which carries a motor 7 coupled bysuit-` able gearing 8 to aspin e 9 on which is mounted a receiving reel10. The wire 11 is fed, from a'delivery reel 12, which is prevented fromover-running by a brake 13.

Geared to the spindle'9 is a spooling cam 16, operating a lever 17 whichconnects by la 4link 18 with a' slide 19 on which the coil box or thewiping device is mounted. By this arrangement, the treated wire isspooled smoothly into placeon the' receivin reel, which'may either betransferred to t e delivery position when filled or by a suitable gearmechanism 4the machine may be reversed and the functions of the tworeels interchanged. This mechanism will not be described in detail here,however, since such devices are well known in the art, are not essentialto the operation of my device, and would complicate the drawingunnecessarily.

The wipin mechanism which is mountable on the sllde 19 comprises a coil31 which is wound on a non-magnetic core 32 provided with end flanges33: The core is conical in form, having a minimum diameter at the endad'acent the delivery spool, and increasing to su stantially the fulldiameter of the end flange at the end adjacent the receivinl spool. One,coil used successfullyconsume about five volt-amperes, giving a totalmagnetomotive force of about one thousand ampere turns. There is a wide.latitude permissible in the design of the coil, depending on the v larguide 34 for holding the wire accurately in the. longitudinal axis ofthe magnetic field 'of` the coil. y

It will be ,appreciated that the field from such a coil is spatiallygraduated, being indecreasin gradually' to nila short distance beyond were the `wire leaves.

Supplying the coill 31 thru the leads 36 is a source 37 of alternatingcurrent. This source may be the ordinary city power su ply, but I preferto use a high frequency oscillator supplying current at a frequency often thousand cycles or more per second.

If the usual sixty cycle power supply is used, the driving mechanismispreferably geared down to move the wire at a much slower rate than thatused for recording andreproduction, and wiping the wire istherefore arelatively slow process.y Thus, if the no1'- mal recording speed is 5feet per second, and

. the reproducing mechanism will respond to frequencies up to fivethousand cycles per.

second, but not to hi her fre uencies, the shortest record wave ength wich will be reproduced will be 5/5000 or .001 foot, and

the record wave length of the wiping. frequency is preferably less thanthis value. If sixty c cle current is used for wipin the record at t erecording speed, the recor wave length would be 5/60 or .083 feet, or 83times the minimum reproducible wave len h, and in order to reduce it -tothe desire value, the record speed must be reduced to less than 1/83rdof the recording s eed. A wiping speed of .O5 feet per secon wouldtherefore be suitablesin this case.

If the high frequency oscillator be used as.y

the source of Wi ing current, the wiping may be accomplishe at therecording speed or even at a greater s ed, as long as the record wavelength is hel below the minimum'. In case sound is being recorded, atwentythousand cycle oscillator may be used to wipe the record atthe'recording speed,'regardless of apparatus limitations, as the averageear ceases t'o function materiallybelow this fre.

uency. With most present types of reproucing a paratus, however,frequencies of over ten t ousand cycles are rejected, and an etic natesthe Aprevious transverse .ppl'arizations forming the recordings. Thiswould obtain even were direct current used' in the coil, and as lon l.asthe wire is' moved truly axially of the coil the net eii'ect is todestroytheltransverse polarizations completely. Since, how-l ever,mechanical imperfections or neighboring magnetic structures may distortthe wiping field to some extent, the alternating current islused, and,as the 'field is graduated, each portion of the wire is subjected 'to aplurality of alternaticns of ma etomotive force of decreasing amplitude,which finally become vanishingly small. The effect of this is' to reducethe polarizations on the wire correspondingly, and thetransversecomponents are thus reduced to a second order infinitesimal. The effectsare further reduced by the of the record, and each is separatelyproducible. Their combination does not produce merely the sum of theindividual effects, but their product, and it is infthis fact that thegreat advantage of the treatment lies.l A record wiped by my method maybe used, for example, to .record the speech of a performer standing manyfeet from the vmicrophone,

' and when reproduced at the original sound level, the voice is notmasked 'by an overwhelming record noise lsuch as has made the magneticrecorder unsuitable for such use inthe past.

I claim:

l. The method of wiping a magnetic record of electrical impulses whichcomprises traversing each portion of the record 'with a graduallyspatially decreasing alternatin magnetic field, said field beingdistributed over a longer portion of the record than the field used tolproduce recordings thereon.

2. The method of wiping a magnetic record of electrical impulses whichcomprises traversing the record with a magneticfield transverse to thedirection of recording polarizations. i

3. The method of wiping a magnetic record'of electrical impulses whichcomprises traversing the record with an alternating magneticeld-transverse to the direction of recording polarizations at a ratesuch that the space traversed during a single cycle is less than therecord wave length of the highest frequency to be reproduced.

4. The method of wiping a magnetic record of electrical impulses whichcomprises traversing the record with an alternating magnetic fieldtransverse to the direction lof the recording polarizations.

5. The method of wiping a magnetic record of electrical impulses whichcomprises traversing the record with a spatially decreasing alternatingmagnetic field transverse to the direction of the recordingpolarizations.

6. A wiper for magnetic records of electrical impulses comprising meansfor producing a substantially uniformly spatially graduated alternatingmagnetic field, and means for moving the record thru said field.

7. A'wiper for magnetic records of elec-4 trical impulses comprisingmeans for producing a substantially uniformly spatially graduatedalternating magnetic field,` and means for moving the record thru saidfield longitudinally thereof.

8. A wiper for magnetic records of electrical impulses comprising a coilhaving a decreasing number of turns perl unit length along 'the axisthereof, and means for movmg the record thru said coil.

" 9. A Wiper for magnetic records of electrica-l -impulses 'comprising acoil having a decreasing number of turns per .unit length along the axisthereof, means for moving the record thru said coil, and a source ofhigh frequency alternating current connected to said coil.

`10. A wiper for magnetic records uof electric impulses comprising acoil having a conical form, and means for moving the record axially thrusaid coil.

1l. A Wiper for magnetic records of elec- I tric'impulses comprising acoil having a conical inner form, and means for moving the recordaxially thru said coil.

In testimony whereof, I have hereunto my hand.

set

CARL w. RHODEHAMEL.

